Wildfires are a natural landscape disturbance in many climates and forest types, but the cumulative impact of human-caused climate change, historical fire management and suppression, and changing species diversity in forests has led to an increase in the size and (or) severity of wildfires in certain regions across the globe. There are a significant number of research studies on the effects of wildfire on human health, forest ecology, hydrology, and the physical, chemical, and biological properties of soils. However, research on the impact of wildfire on watersheds including toxicity in aquatic organisms, water chemistry, and fluvial sediment quality is less extensive, focusing primarily on water quality indicators such as nutrients and sediment flux. Recent research has shown that wildfires contribute to the environment significant amounts of polycyclic aromatic hydrocarbons (PAHs), which are compounds produced during the incomplete combustion of organic material, and are known to be toxic and mutagenic compounds. The primary objective of this paper is to review the recent literature that pertains to the contamination of surface waters and sediments and source apportionment of wildfire-derived PAHs to determine where research gaps remain. Additional objectives are to assess the use of molecular ratios to apportion PAH sources and, finally, to create a roadmap for future studies in designing and conducting research that seeks to determine sources of wildfire-derived PAHs in water and sediment.

Purpose: This research aimed to determine if a severe wildfire caused changes in the source of sediment being delivered to downstream aquatic systems and evaluate the use of polycyclic aromatic hydrocarbons (PAHs) and color properties as tracers. Methods: Sediment samples were collected from 2018 to 2021 in three tributaries impacted by the 2018 Shovel Lake wildfire and from two sites on the mainstem of the Nechako River, British Columbia. Source samples were collected from burned and unburned soils as well as from channel banks and road-deposited sediment. Samples were analyzed for color properties and for the 16 US Environmental Protection Agency priority PAHs. After statistical tests to determine the conservatism and ability to discriminate between sources by the tracers, the MixSIAR unmixing model was used, and its outputs were tested using virtual mixtures. Result: In the tributaries, burned topsoil was an important contributor to sediment (up to 50%). The mainstem Nechako River was not influenced as significantly by the fires as the greatest contributor was banks (up to 89%). The color properties provided more realistic results than those based on PAHs. Conclusion: In smaller watersheds, the wildfire had a noticeable impact on sediment sources, though the impacts of the fire seemed to be diluted in the distal mainstem Nechako River. Color tracers behaved conservatively and discriminated between contrasting sources. Due to their low cost and reliability, they should be considered more widely. While PAHs did not work in this study, there are reasons to believe they could be a useful tracer, but more needs to be understood about their behavior and degradation over time.

Background: The Nechako River Basin (NRB) is a large, regulated basin in north-central British Columbia, Canada that has been impacted by numerous landscape disturbances, including a severe wildfire in 2018. Aims: The aims of this study were to quantify the post-wildfire temporal and spatial extent of contamination by polycyclic aromatic hydrocarbons (PAHs) of both soils and riverine sediments, and to identify the primary sources of PAHs in the watershed. Methods: Soil samples were collected at burned and unburned sites in 2018 and at the burned sites in 2020 and 2021. Sediment samples were collected at three tributaries impacted by wildfire and three Nechako River mainstem (i.e. main channel) sites from 2018 to 2021. Samples were analysed for parent PAHs. Key results: PAH concentrations decreased in soil samples from 2018 to 2021 but are not below the concentrations found in unburned samples. Tributary sediment samples showed higher concentrations immediately post-fire relative to the mainstem Nechako River, but in the years since, that trend has reversed. Conclusions: PAHs persist in terrestrial and aquatic environments for years following wildfire, but at concentrations below various quality guidelines. PAHs were primarily derived from the wildfires, with some mixed sources at the downstream sites. Implications: Wildfires are an important source of environmental contamination of terrestrial and aquatic environments.

Smart growth promotes urban sustainability by encouraging increased densities, mixed use, walkable design, and access to diverse transportation and housing options. This study applies literature-derived indicators to examine urban change in the city of Prince George; British Columbia’s northern capital. Findings illustrate that key growth nodes have largely performed (e.g., densified) at or below the level of their surrounding neighbourhood over time despite a robust set of policy tools associated with smart growth. This research is one of few to examine smart growth in a northern urban context, and situates the concept within the slow growth/no growth realities of many rural and remote regions.

Vegetated filter strips (VFS) are a best management practice, designed to reduce sediment and nutrient runoff to surface waters in agricultural landscapes. In cold climates, phosphorus (P) can be released from VFS vegetation when it undergoes freeze–thaw cycles, making their utility in these regions an area needing further study. Research in Manitoba, Canada, investigated temporal changes in soil P concentrations and potential P loss from VFS from 2015 to 2017. Soil, harvestable vegetation, and residue samples were collected within VFS and control strips, and soils were analysed for Olsen P and Total P (TP). Harvestable vegetation and residue samples were analysed for TP. Results showed increases in Olsen P each spring and reductions each fall in soils at all sites. There was substantial loss of TP from the harvestable vegetation samples at all sites from November 2016 to May 2017, but residues in the VFS and control sites had a lower loss of TP over the same period. Vegetation was shown to release P over the winter into surface soils, and harvestable vegetation released significantly more P than residue, potentially leading to P loss from soils through surface runoff or leaching. Thus, harvesting vegetation may be a suitable VFS management strategy in cold climates.

Across North America the area burned by wildfire is steadily increasing, and these fires have significant impacts on terrestrial and aquatic ecosystems. Of particular concern are the contaminants that are produced during wildfires when biomass and structures burn. One class of contaminants of concern is polycyclic aromatic hydrocarbons (PAHs), which can be mutagenic, carcinogenic, and toxic for certain species. This study measured concentrations of PAHs in the burned topsoil and the burned organic layer in eight wildfires of varying ages across the interior of British Columbia, Canada. Samples were analysed for the 16 U.S. Environmental Protection Agency (EPA) Priority PAHs and for 30 alkylated PAHs, the latter of which are often more toxic and difficult to break down. Results showed that within three to six years after wildfire the concentrations of ΣPAHs returned to concentrations similar to reference sites. The year post-fire that the sample was collected showed a strong correlation to the ΣPAH concentrations, and comparisons across all samples showed that characteristics associated with the fire's biogeoclimatic zone explained most of the variability. Soil quality guidelines were not available for all compounds analysed, but concentrations for many of the samples exceeded available guidance. Coupling post-wildfire landscape susceptibility to erosion and the hydrophobicity of PAHs, the threat to water quality in burned areas is significant. More post-wildfire erosion mitigation on hillslopes should be undertaken to avoid negative impacts on the aquatic environment, particularly in the British Columbia interior where salmon are already under numerous anthropogenic and environmental pressures.